To fully support hydrogen code stubs which accept a variable number of arguments,

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2540 matching lines @@
       __ movsd(XMMRegister::FromAllocationIndex(save_iterator.Current()),
                MemOperand(rsp, count * kDoubleSize));
       save_iterator.Advance();
       count++;
     }
   }
   if (NeedsEagerFrame()) {
     __ movq(rsp, rbp);
     __ pop(rbp);
   }
-  if (info()->IsStub()) {
-    __ Ret(0, r10);
+  if (instr->has_constant_parameter_count()) {
+    __ Ret((ToInteger32(instr->constant_parameter_count()) + 1) * kPointerSize,
+           rcx);
   } else {
-    __ Ret((GetParameterCount() + 1) * kPointerSize, rcx);
+    Register reg = ToRegister(instr->parameter_count());
+    Register return_addr_reg = reg.is(rcx) ? rbx : rcx;
+    __ pop(return_addr_reg);
+    __ shl(reg, Immediate(kPointerSizeLog2));
+    __ addq(rsp, reg);
+    __ jmp(return_addr_reg);
   }
 }
 
 
 void LCodeGen::DoLoadGlobalCell(LLoadGlobalCell* instr) {
   Register result = ToRegister(instr->result());
   __ LoadGlobalCell(result, instr->hydrogen()->cell());
   if (instr->hydrogen()->RequiresHoleCheck()) {
     __ CompareRoot(result, Heap::kTheHoleValueRootIndex);
     DeoptimizeIf(equal, instr->environment());
@@ skipping 3259 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64